The present invention is directed to a method and system for automatically controlling lighting in a space.
In order to reduce energy consumption in office buildings, a number of different occupancy-sensing schemes have been developed to automatically control illumination levels depending on whether a space is occupied or not. Typically, the light level within a space is reduced when it is sensed that there is little or no activity within that space. This is often as simple as installing automatic “on-off” controls in each room.
These methods typically are implemented only in small rooms and private offices where occupancy can be distinctly determined and are seldom applied to larger public areas because they drastically impact the quality of lighting to the point of being deemed unacceptable. For example, areas such as cafeterias, cubicle office arrays, warehouses, and retail and department stores even when not directly occupied are still “on display.” Dimming the lighting levels in such areas could present an uninviting, unsafe or closed-for-business atmosphere. Moreover, the energy-saving purpose is defeated if the lighting level for an entire large area must be increased when sporadically used by a low number of occupants.
Thus, the need exists for a system and method for controlling lighting that is suitable for large common areas and that avoids the problems of the prior art.
The following terms are used herein.
Illumination level is a measure of the amount of useable light which is incident on a surface, generally measured in units of luminous intensity per unit area.
Color rendering index (CRI) is a measure of the quality of light emitted by a light source with regard to its ability to effectively reproduce the color of an illuminated object. It is also indicative of the spectral characteristics of the emitted light. More particularly, CRI is a measure of the amount of color shift that objects undergo when lighted by a light source as compared to the color of those same objects when seen under a reference light source of comparable color temperature. CRI is expressed on a scale of 0-100, where 100 is the best for producing colors that are natural and vibrant.
Correlated color temperature (CCT) is a description of color appearance of a light source in terms of its warmth or coolness, measured in Kelvin (K). Lamps with a low CCT (3000K or less) generally have a yellow-white color and are described as “warm,” while lamps with a high CCT (4000K or higher) have a blue-white color and are described as “cool.”